Example #1
Fred: "I can't believe this store stops selling beer at 9 pm. What are we going to do?"
You: "Brain wave! The one down on Jeff Davis Hwy sells until 11! Get in the truck and let's roll!"
Fred: "You are a genius!"

Example #2
Bob: "My car stopped working, how are we going to get to the show?"
You (again!): Brain wave! My neighbor always leaves the keys in his ignition. Let's roll!"
Bob: "You are a genius!"

A brain wave is a stupid thought that some kind of idiot gets after a sleepless night. This brain wave can become a brain Tsunami when this idiot is some kind of boss.
A brain farth is also some kind of idea.

Good examples of brain waves can be found in politic environments, for instance: "What about attacking Iran with nuclear bombs ?"

When you are receiving oral pleasure (fellatio) and when you are about to blow your wad, you cum in her nose which feels like when you dive in a pool incorrectly and all that water gets into your sinuses and hurts, thus the name brainwave.

Dude, I was getting blown by Jessica and i just felt like giving her a brainwave, she passed out, then I gave her another one.